WASHINGTON — Blood banks turn away up to 150,000 would-be donors each year on the slight chance they picked up malaria while traveling to any of dozens of countries.

At the same time, concern is growing that a second parasitic infection from abroad — the Chagas disease rampant in parts of Latin America — increasingly threatens donated blood.

Both infections are rare here, but there’s no way to test donated blood for either one. Now blood banks are pushing for better safeguards that also could help stretch the nation’s tight supply.

First up, malaria: This week, the Food and Drug Administration opens debate on how to balance the need for blood with Americans’ increasing travel to malaria hot spots, and to urge manufacturers to develop a malaria test to solve the problem.

The vast majority of U.S. travelers return healthy, and there have been only one or two cases of transfusion-spread malaria in five years. But without a blood test, there’s no way to tell who might be unknowingly incubating the mosquito-borne disease.

So FDA requires blood banks to ask about would-be donors’ travels. No donating for a year after a short trip to a malaria-prone country; for three years for anyone who spent more than a year in a malaria-prone country or suffered malaria symptoms.

It doesn’t matter if you faithfully took anti-malaria medicine; you could have forgotten a missed pill or be one of the unlucky few infected anyway. Staying in a cruise ship or large resort is OK in some countries, unless you took even one trip inland, even during daytime hours when mosquitoes seldom fly.

Even “safe” vacation spots may not be: The Bahamas aren’t normally malaria-prone, but a May outbreak has just put tourists returning from one island, Great Exuma, on the no-donation list, too.

'Losing a lot of blood'
"When you’re talking about an entire nation, in the end, you’re losing a lot of blood,” says Ben Nefzger, 72, of Rock Island, Ill., who has donated blood several times a year for decades but was turned away for the past year because he spent five months teaching in a Sierra Leone seminary.

Some 34,000 pints of blood are needed every day, yet only about 5 percent of the Americans eligible to donate do so, and increasing foreign travel is further shrinking that donor pool. The American Red Cross, which collects half the nation’s blood, last year estimated that some of its regions were losing 150 to 200 donations a month because of the malaria risk.

“To get these donors to come back is not easy,” laments Dr. Celso Bianco of America’s Blood Centers, a group of independent blood banks that collects the other half of the supply.

Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

Historically, most cases of transfusion-spread malaria have been traced to immigrants from malaria-prone countries who still harbored the parasite despite years with no symptoms, something only a test could uncover, he adds.

One U.S. manufacturer, Abbott Laboratories, is in the initial stages of designing a malaria test for donated blood.

Britain and parts of Europe already allow travelers to donate if blood tests show they’re free of malaria antibodies, immune cells that attack the parasite. Those tests aren’t used here because they detect just two of the four malaria species, albeit those that cause most disease. On Tuesday, FDA will ask specialists if that’s still good policy.

“We may have to be open-minded about that,” says Dr. Hira Nakhasi, FDA’s director of emerging transfusion-related diseases.

For Chagas, a test for donated blood could arrive by year’s end, one blood banks anxiously await as they seek more donors from a growing Hispanic population.

Up to 19 million infectedChagas infects up to 18 million people in parts of rural Mexico, Central and South America, and kills 50,000 of them yearly. Most don’t know they’re infected: The parasite can lie silent for decades, until one day erupting inside the heart, esophagus or intestine.

It’s spread mostly by “kissing bugs” that live in the cracks of thatch-roofed, mud-walled homes, crawling out at night to bite sleepers. But it’s also spread from mothers to their unborn children, and through blood transfusions.

There have been five transfusion-spread Chagas cases in the U.S. and two in Canada — “that we know of,” says Red Cross Chagas expert Dr. David Leiby. Because it lies dormant for so long, “there probably are other transfusion cases going on that aren’t recognized.”

How many is hard to say. Leiby’s research in the late 1990s estimated one in 25,000 donors overall may carry Chagas disease, but as many as one in 5,400 in Los Angeles with its high Hispanic population. No one knows how many carriers actually harbor enough parasite in their blood to infect someone.

FDA’s Nakhasi says the agency will mandate a Chagas test for every blood donation as soon as it’s convinced there’s a good method. First in line may be a test developed by Ortho-Clinical Diagnostics, currently under FDA review; competitor Abbott is researching another version.